1. Field of the Invention
The present invention relates to image processing apparatus, and more particularly, to an ultrasonic diagnostic apparatus which transmits an ultrasonic wave into a patient and obtains diagnostic information inside the patient on the basis of the ultrasonic wave reflected from the inside of the patient, and an ultrasonic image processing apparatus which uses an ultrasonic image obtained by the ultrasonic diagnostic apparatus.
2. Description of the Related Art
In the ultrasonic diagnostic inspection, a heartbeat or a fetus's movement state may be obtained in real time just by touching a body surface with an ultrasonic probe and the ultrasonic diagnostic inspection may be repeated due to the reliability of the ultrasonic diagnostic inspection. In addition, since the system size of the ultrasonic diagnostic apparatus is smaller than those of other diagnostic apparatuses such as an X-ray diagnostic apparatus, a CT diagnostic apparatus, and an MRI diagnostic apparatus, the ultrasonic diagnostic inspection may be easily performed by disposing the ultrasonic diagnostic apparatus on the side of the bed. For this reason, the ultrasonic diagnostic inspection is a simple diagnostic method. Although the size of the ultrasonic diagnostic apparatus used in the ultrasonic diagnostic inspection is different depending on the types of the functions thereof, a small-sized ultrasonic diagnostic apparatus which can be carried by one hand is developed. Unlike the X-ray diagnostic apparatus, the ultrasonic diagnostic inspection is not influenced by an exposure, and may be used in the obstetrics and gynecology or home medical treatment. In such an ultrasonic diagnostic apparatus, generally, a two-dimensional tomographic image is obtained by scanning a specific section of the patient using an ultrasonic probe having ultrasonic vibrators arranged in one dimension. However, in recent years, three-dimensional biological information (volume data) can be collected by spatially scanning the inside of the patient using a two-dimensional array ultrasonic probe having ultrasonic vibrators arranged in two dimensions.
However, the received signals obtained from the plural adjacent patient tissues interfere with each other due to the phase information thereof, and an image pattern obtained by a viewing method different from the case of synthesizing only the amplitude information, that is, a speckle pattern is created. Since the speckle pattern often disturbs an operation of accurately observing the shape and position of the boundary of the patient tissue, various treatment methods of removing the speckle pattern are proposed.
As one method, there is known a method in which a target image is subjected to a multi-resolution decomposition by means of a Wavelet transform and a Wavelet inverse transform, and the respective decomposed images are subjected to a predetermined process. The multi-resolution decomposition and the multi-resolution reconstruction are used to reduce the noise of the image or to synthesize plural images without appearing unnatural. For example, as disclosed in JP-A-2000-224421, for the purpose of removing a noise, the Wavelet multi-resolution decomposition through several levels is performed, an opening and closing process based on a mathematical morphology is performed on a low-band component of the decomposed image, and then a difference therebetween is obtained to extract a noise component. Then, a noise removing process is performed on the basis of the result, and the obtained image is provided to the next level decomposition.
As another method, as disclosed in JP-A-2007-256338, for the purpose of improving a resolution by removing a discontinuous feeling at a boundary between an overlapped region and a non-overlapped region upon synthesizing plural sheets of images having an overlapped region obtained by a compound scanning method in the ultrasonic diagnostic apparatus, plural sheets of images to be synthesized are subjected to the multi-resolution decomposition, and the decomposed images are subjected to a filter calculation process such as an average and a maximum value of the plural sheets of images.
In addition, the compound scanning method is one of the speckle pattern removing methods, but in the speckle pattern removing method not based on the scanning method, a filter process may be performed on the high-band component of the image having been subjected to the multi-resolution decomposition.
Meanwhile, for the purpose of extracting a shape or reducing a noise, a method called a morphological reconstruction is known as disclosed in H. Arefi, M. Hahn “A Morphological reconstruction algorithm for separating off-terrain points from terrain points laser scanning data”, ISPRS WG III/3, III/4, V/3 Workshop “Laser scanning 2005”, Enschede, the Netherlands, Sep. 12-14, 2005 or “Morphological Reconstruction”, MathWorks, Inc. http://www.mathworks.com/access/helpdesk_r13/help/toolbox/images/morph10.html.
However, the known speckle pattern removing method has problems as below.
That is, according to a simple process such as a threshold value setting and a weighted value or the morphological opening and closing process used in JP-A-2000-224421, it is possible to reduce the speckle pattern. However, the resultant image gives an artificial feeling to an observer.
Further, according to the morphological reconstruction process, it is possible to obtain an image in which a regional maximum value is reduced and a bright portion of the speckle pattern is cut. However, a dark portion of the speckle pattern is not removed only by the morphological reconstruction process, and hole shapes are formed at several positions on the image. In addition, since the speckle pattern reduced portion is not smooth, the boundary and the uneven portion are visibly noticed.